Each year literally millions of consumer appliances, such as washing machines, are manufactured and sold in the United States. To keep pace with consumers' increasing desire for new features and in order to properly care for the various types of fabrics and garments being sold today, the complexity of the control circuitry for such appliances continues to increase. At the same time, however, the increasing governmental requirements for energy efficiency and the consumer and competitive pressures to keep costs down have added increased stress on the design and manufacture of these appliances. Indeed, with consumer preferences often driven by costs and quality, as opposed to traditional brand loyalty, manufactures must ensure that their appliances are competitively priced and operate properly when purchased and installed by a consumer. As is recognized by such manufactures, any defect or failure to operate of a consumer appliance once purchased and installed will likely result in negative word of mouth severely impacting sales.
As such, manufactures have realized that one-hundred percent quality control has become an absolute necessity, particularly when so many appliances are manufactured each year. That is, settling for a quality control threshold of ninety-nine percent, and assuming for the sake of this example that one million units are produced, this ninety-nine percent quality control will result in 10,000 defective consumer appliances being sold and installed by consumers, who will then share their negative experiences with their friends and family. This is simply unacceptable.
To prevent such occurrences from happening, many consumer appliance manufactures now require one-hundred percent testing of all manufactured appliances before they are released from the factory for sale to consumers. Washing machines, for example, are connected to water and electrical supplies, and washing cycles are completed during the final assembly process of the appliance. In this way, any defects in the manufacturing process, will be identified and rectified before that particular unit is released for sale.
Unfortunately, to ease the ability of correcting any problems in the manufacturing process, each appliance is run before the final assembly is complete. For example, such quality testing may be begun and continue prior to final securing of the control panel of the appliance to the mounting panel of the washer.
It has been observed that occasionally during this quality testing and final assembly operation that faults have occurred in the control wiring of the appliance. Such faults, for example contact welding, may be attributed directly to excessive shock and vibration that may occur due to the excessive shock and vibration to which the entire appliance is subjected while moving down the conveyor system in the assembly plant while being tested. Such failure significantly increase the overall cost of manufacturing, and may result in failed units being released for customer sale if the high shock failure occurs at the end of the testing cycle.
For washing machines, such as top loading washing machines, one common failure that can be directly attributed to the high vibration or shock seen during the final stages of the manufacturing process as the washing machine is being quality tested is a contact welding problem resulting from a dead short between the L1 and neutral (N) sides of the 120 volt AC lines that power the washing machine. Specifically, many top loading washing machines utilize a mechanical timer to switch the L1 and N sides of the 120 volt AC lines to change the direction of the main drive motor in the washing machine.
In such designs, e.g. shown in FIG. 1, the timer typically uses two single pole double throw switches, shown as switching assembly 102 to accomplish this reversal by reversing the L1 and N connections to the starting winding 104. Such switching assemblies 102 are typically wired with a neutral line on one side of the center contacts 112, 114, and the L1 line on the other side of the center contacts 112, 114. Such switches are designed to have only one side of this switch made, or the other, i.e. contacts 116 and 122 closed, or contacts 118 and 120 closed. However, if the appliance sees a high shock or vibration while the timer is powered, the applicants have discovered that such high shock or vibration can cause the contacts 116, 118, 120, and 122 of the switching assembly 102 to bounce in such a manner that three or four of the contacts touch, which causes a dead short between the L1 and neutral sides of the 120 volt AC lines through the switching assembly 102. Such a dead short will typically result in the main circuit break on the assembly line power source to trip, possibly a tripped circuit breaker 124 in the motor through which this high current flows, and can cause welded contacts of the switching assembly 102.
If this fault occurs at the end of the quality testing cycle, it may go undetected and the washing machine may be released for sale to a consumer. However, once installed by a consumer, the washing machine will not operate properly and will require a service call to replace the timer and/or reset the circuit breaker. Not only will this result in a negative consumer experience, but it also increases the manufacture's warranty service costs and reduces the manufacture's quality reputation.
In view of the above, there is a need in the art for control circuitry for a consumer washing machine that enables multi-cycle operation while avoiding catastrophic contact welding failures resulting from the high shock and vibration experienced during the quality control testing phase of final manufacturing of the appliance, or vibration in the home caused, e.g., by severe off balance loads. Embodiments of the present invention provide such a control system and circuitry. These and other advantages of the invention, as well as additional inventive features, will be apparent from the description of the invention provided herein.